Recent years have been marked by a considerable interest in the synthesis and studies of liquid crystalline (LC) and amorphous polymers containing azo dye fragments in the side chains. Those polymers were convincingly shown to be applicable for reversible optical high density data recording and for data storage systems with optical memory [1-6].
The principle of photooptical recording is based on the activation of photochromic azo dye side branches of various homo- and copolymers under the action of the light with a certain wavelength. Those azo dye fragments undergo a series of photochemical configurational transformations (trans--cis isomerization) which cause their conformational changes: the rod-like azobenzene groups in the trans-conformation rearrange to the cis-isomers having a bent (broken) form. Such transformations lead to the local changes in orientation of not only photo chromic monomer units but also the neighbouring non-photo chromic mesogenic side groups. The probability of light absorption by photo chromic fragments is different, so the photo chromic side branches must aquire a predominant orientation due to photoselection. If polarized light is used, the azo fragments are oriented in such a way that the long axis of the dye fragments are perpendicular to the electric vector of the light (or laser illumination). This process is accompanied by the orientation of the neighbouring side groups in the amorphous polymers and the reorientation of the neighbouring mesogenic groups in the LC polymers; in other words, the cooperative orientation of photo chromic and non-photo chromic groups takes place. Thus, the light acts as a "controlled external field" permitting us to regulate the supramolecular structure of the polymer and to obtain high-oriented polymer materials at ambient temperature.
The orientation of asymmetric side fragments of amorphous and LC polymers results in a significant appearance of photoinduced birefringence, .DELTA.n.sub.ind. The values of .DELTA.n.sub.ind essentially depends on the initial structural organization of the polymer matrix: the higher degree of the mesogenic groups ordering, the less values of the photoinduced birefringence, since the orientational order in the LC state most likely restricts the reorientation of side groups and, therefore, that process is probably more effective in the less ordered medium.
Up to date mainly nematic and smectic photo chromic azo dye containing copolymers have been used for photo optical investigations [1-9].
Previously known photo optic polymers are generally of the type of highly viscous liquids and require a covering glass to be able to be used after the polymers (viscous liquid) have been orientated. This is a great disadvantage as there is no mechanical strength at all present in the polymers.